Why does gravity only attract?

Gravity only attracts because energy always makes light rays passing through a region converge. In OPH every small region that has finished settling holds the most entropy its boundary allows. When energy enters, the entropy of the contents rises by that energy, read on the region's own clock. The boundary's share has to fall by the same amount, so its area shrinks, and light rays crossing the region bend toward each other, the way two walkers heading due north from the equator meet at the pole. That focusing is the pull. The step assumes that the number of links crossing the boundary measures the physical area, that the region's clock is a physical clock and that a settled region is in physical equilibrium, and OPH's finite model does not yet establish these. Whether a particle's upkeep enters the balance exactly as heat and light do is still open. Any answer must match equivalence tests, which find no difference in how titanium and platinum fall at one part in 10¹⁵.